The subject matter of this application relates to a device that selectively attaches to the prongs of an electrical plug and provides a visual indication of a voltage across the prongs.
Some modern electrical extension cords often include indicator lights indicating the presence of power in the extension cord. For example, U.S. Pat. No. 4,671,597 to Grill discloses an extension cord having a female receptacle into which the prongs of an electrical plug may be inserted. The female receptacle includes a lamp connected to respective conductors wired to the hot and neutral prongs of a male plug at the opposite end of the extension cord, so that the lamp is illuminated when the extension cord is plugged into an outlet. These same conductors are positioned so that they contact the hot and neutral prongs of any plug inserted into the extension cord. The reason for the indicator lamp of Grill is that extension cords often extend around walls or other obstacles that prevent a person from knowing whether the extension cord is plugged into an outlet at the time it is being used. The indicator lamp provides this indication.
Also, many existing power strips have indicator lights indicating the presence of a voltage potential at any (or all) of the sockets provided by the power strip. For example, some power strips include a switch that alternatingly provides voltage to all the sockets in the power strip or disables voltage to all the sockets in the power strip; a light indicates which of these two states the switch is set to. Still other power cords include such switches and/or lights to each of the sockets in the power strip. Again, as above with respect to the extension cord of Grill, the indicator lights provide an easy indication of the presence of power to the power strip's sockets.